Ceramic packing material for the prevention of methacrylate and acrylate ester polymerization



United States Patent 5 Claims. (Cl. 252-397) This application is adivisional application of copending application Ser. No. 417,504, filedDecember 10, 1964, now Patent No. 3,332,984 which is, in turn, acontinuation-in-part of application Ser. No. 124,799, filed July 18,1961, now abandoned.

This application relates to an improved method for the production ofmonomeric methacrylate and acrylate esters.

It is known that acrylic amides can be converted to esters by reactionat elevated temperatures with an appropriate alcohol in the presence ofwater and a strong acid, preferably a mineral acid such as sulfuricacid. Methacrylamide reacts under these conditions, for example, withmethyl alcohol, butyl alcohol, etc. to give the corresponding alkylmethacrylates. However, it has been found that esters of this kindpolymerize so readily that process equipment becomes plugged withpolymeric material and keeps the yield of monomers at relatively lowlevels. To overcome this disadvantage, it has been proposed to employwell known polymerization inhibitors such as hydroquinone,diphenylamine, phenol, pyrogallol, tannic acid, copper, sulphur andother compounds of similar nature. Air and oxygen have also beenproposed as inhibitors. While these compounds decrease the amount ofpolymer formed, they do not completely eliminate it, especially inprocesses employing packed reactors and packed distillation columnswhere the conditions are such as to prevent the use of organicinhibitors and, therefore, require inorganic inhibitors which are lesseffective than organic inhibitors.

We have now found that polymerization of methacrylate and acrylateesters in the preparation of the monomeric ester compounds in processequipment such as packed distillation columns and packed reactors isprevented by using ceramic packing therein which has been treated with astrong mineral acid and more especially a nitric-sulfuric acid mixture.The eifective life of the thus treated packing is so great that nodecrease in activity, i.e. prevention of polymerization, was found aftertwo months of continuous operation of such process and equipment.

It is, accordingly, an object of the invention to provide an improvedprocess for the preparation of monomeric methacrylate and acrylateesters. Another object is to prevent polymerization of said esters inthe process and purification of the same. Another object is to provide anovel acid treated packing material that prevents polymerization of thesaid monomers during processing of the same. Other objects will becomeapparent hereinafter.

In accordance with the invention, we prevent the polymerization ofmonomeric methacrylate and acrylate esters in the preparation andpurification thereof by packing the distillation column of the reactorwith ceramic materials ordinarily used as a packing but which have beenfirst treated with a mixture of strong mineral acids or other compoundsthat produce oxides of nitrogen under the conditions leading to bondingor absorption of the oxides of nitrogen or their ions or radicals to theceramic packing. It is of particular significance that the ostensibly"ice equivalent procedure of introducing oxides of nitrogen into thecolumn or the reactant feeds rather than to treat the packing materialis in fact quite ineffective in preventing polymerization in the reactoras illustrated by the following experiment:

A glass column 48 inches long and 1.61 inches in diameter containingcubic inches of A inch unglazed prolelain Berl saddles was heated with aChromel wire-wound jacket. The lower end of the column was maintained atabout IDS-115 C. and the upper end at about 101-110 C. A 2-literreboiler (base heater) containing a water solution of ammonium acidsulfate and sulfuric acid maintained at about 112-124 C. was connectedto the bottom of the column. Methacrylamide prepared by the amidesynthesis from 2,810 ml. of acetone cyanohydrin and 3,660 ml. of percentsulfuric acid was fed at a substantially constant rate during the courseof 17.3 hours into the top of the column maintained at about 98105 C.along with 8,200 ml. of water. 10,225 ml. of isobutanol was vaporized at108 C. and fed to the reboiler at a substantially constant rate alsoduring the course of said 17.3 hours and was carried up the column withsteam fed into the reboiler via a water vaporizer. As the amide acidsolution flowed down the reactor it reacted with the alcohol vapor andproduced the methacrylate ester. The ester was vaporized and carried outof the column into a decanter along with unreacted alcohol and water.The co-product ammonium acid sulfate flowed down the column to thereboiler where it was removed through a drain. Substantial amounts ofnitric oxide was added to the methacrylamide-feed solution and also tothe reboiler in carrying out the above process. Sufficient nitric oxidewas added to the methacrylamide-feed solution to saturate the same withnitric oxide, and nitric oxide was fed to the reboiler at approximately20 ml. (S.T.P.) per minute. Air was also introduced into the reboiler at50 to 100 ml. per minute in an attempt to further inhibitpolymerization. At the end of said 17.3 hours of operation, the reactorbecame completely plugged with polymer and was thus rendered totallyineffective.

The treatment of the ceramic packing is carried out conveniently bysoaking the packing in a nitric-sulfuric acid mixture for several hours,removing the acid mixture, and then washing the so treated packing withwater. The acid concentrations for both the nitric acid and the sulfuricacid may be varied from the strength of commercial concentrated acids tofuming acids containing varying amounts of the free anhydrides, forexample, concentrated nitric acid containing free N0 and concentratedsulfuric acid (oleum) containing free S0 In the case of the latter, theS0 content may be for technical grades up to 66%, while a content ashigh as 90% is known. The ratio of nitric to sulfuric acids is notcritical as long as appreciable amounts of both acids are present in theacid mixture. Actually any mixture of acids or other compounds thatproduce oxides of nitrogen can be used; for example, a mixture ofconcentrated sulfuric acid and various salts of nitric and nitrous acidssuch as nitrates or nitrites. The preferred acid mixtures for treatingthe packings employed in the invention comprise combinations ofconcentrated sulfuric acid or oleum and concentrated nitric acid. Atypical mixture comprises equal volumes of the concentrated acids.Another efficacious mixture comprises equal volumes of concentratednitric acid and oleum containing 20 percent of S0 The temperature of themixtures as used for treating the packing also is not critical, butgenerally in the range of about 15-60 C., and preferably at or aboutnormal room temperatures of 20-30 C. The time of treatment should besufficient to activate the packing, but advantageous results areobtained with treatment periods as low as 15 3 minutes and up to 1224hours; however, no additional advantage appears obtainable by prolongedtreatments.

Suitable ceramic packing that can be treated according to the inventionincludes any ceramic materials used as packing for one reason or anotherin chemical reactions and columns. The term ceramic, as used in thedescription, is meant to apply to porcelain and stoneware productsprepared from varying amounts of clay, flint and feldspar. Porcelain andstoneware differ primarily in porosity. Chemically speaking, ceramicmaterials are composed of aluminum silicate, silica and potassiumaluminum silicate so that any material containing these or analogouscomponents would be operable in the invention whether called ceramics,porcelain, stoneware, etc. or not. Thus, packings now known which can beused efficaciously in the practice of our invention include ceramic orceramic-like shaped articles known in the art under the names of Raschigrings, Lessing rings, Cross-partition rings, Spiral rings, Intaloxrings, but more particularly Berl saddles which is the preferredpacking. Actually, the packing to be treated can be in any shaped formdesired, the object being to bring the treated and activated ceramic orceramic-like material in intimate contact with the monomer liquid and/orvapor. This can be carried out in any conventional equipment thatutilizes a packing in the processing of methacrylate and acrylateesters. Advantageously, the equipment comprises a tubular reactor andfractionating column packed with the mentioned ceramic packing materialswhich have been treated in accordance with the invention, and providedwith conventional heating, feeding withdrawal and refluxing means, butpreferably having the amide feed enter the upper region of the columnand the alcohol feed enter the lower region of the column, the formedesters passing overhead to a condenser while sulfuric acid or other suchstrong acid, water and ammonium salts are removed from the base througha drain connected at the base of the column.

In carrying out the process of the invention, the reactants comprisingmethacrylamide or acrylamide, alcohol, a strong acid selected from thegroup consisting of H 50 HCl and H PO with sulfuric acid beingpreferred, and water, are passed into the reactor column containing theacid treated ceramic packing material. The useful strong acids maygenerally be defined as those which ionize in water essentially 100% togive hydronium ions and the acid anion. The amide feed containing thestrong acid is preferably passed in liquid form into the column at ornear the top of the column, and the alcohol feed and water feed ispassed into the column at or near the base of the column, while thestrong acid, water and ammonium salts are removed from the base througha suitable drain. The water is preferably added to the base reboiler inthe form of steam. Advantageously, phenolic inhibitors such as phenol,cresol,-etc. and air are also added to the column, the former at the topsection and the latter at the bottom section to inhibit polymerizationin the reboiler section of the reactor column. However, these types ofinhibitors are wholly ineffective by themselves in preventingpolymerization of the unsaturated monomers in the esterification andfractionating sections of the column. While the invention is applicableto batch processes, it is primarily adapted to a continuous mode ofoperation wherein the addition and withdrawal of materials are carriedout continuously and so regulated as to balance one another. The columnneed be shut down only at intervals of several weeks or more to replacewith freshly mixed acid treated packing, Whereas in similar operationsemploying untreated packing, scvere clogging of the column from polymerformation therein occurs in about a day or less of operation.

The following examples will serve to illustrate further the manner ofCarrying out the process of the invention.

4 Example 1 This example is for comparison purposes and illustrates thevery much improved results obtained by the process of the inventionemploying a ceramic packing material pretreated with a mixture of nitricand sulfuric acids in the reactor column as compared with the resultsobtained with the untreated ceramic material under the same conditionsof reaction.

The reactor employed in the following Experiments A and B consisted of aglass column 48 long and 1.61" in diameter containing cubic inches of Aunglazed porcelain Berl saddles. The reactor was heated with a Chromelwire-wound jacket. Isobutanol was fed into the 2-liter base heater witha Cerveny micro-bellow pump. Air was introduced into the base at ratesof 50-100 ml. per minute as a polymerization inhibitor. Aqueousmethacrylamide containing sulfuric acid was fed to the top of thereactor while a preheater was used on the alcohol feed to the base. Adecantor separated water from the crude product. Sulfuric acid, water,and ammonium salts were removed from the base through the drain. InExperiments C and D, the reactor was increased in size to 72" x 2.0" andcontained 220 cubic inches of 4" unglazed porcelain Berl saddles.

A. Aqueous methacrylamide prepared in the amide synthesis form 2,810 ml.of acetone cyanohydrin and 3,660 ml. of percent sulfuric acid was fedinto the top of the reactor with 8,200 ml. of water while 10,225 ml. ofisobutanol was fed to the base heater all during the course of 15.8hours. Phenol and air were also fed into the reactor during this time toinhibit polymerization in the reboiler section of the reactor. A totalof 5,124 g. of crude organic product was obtained from the decanter whenthe reactor column become plugged with polymer. This is equivalent to56.8 grams of organic product per cubic inch of Berl saddles.

B. The reactor packing was then replaced with A" unglazed porcelain Berlsaddles which had been treated as follows:

Clean Berl saddles were covered with a mixture prepared f-rom equalvolumes of fuming sulfuric acid (20 percent sulfur trioxide) andconcentrated nitric acid. After 12 hours, the acid mixture was pouredoff and the saddles were washed twice with water.

The reactor was run as before feeding methacrylamide obtained from thereaction of 32,770 ml. of acetone cyanohydrin and 37,160 ml. of 100percent sulfuric acid along with 34,980 ml. of water and 90,000 ml. ofisobutanol during the course of 162.1 hours. Phenol and air were addedas in above A. During this time, there was obtained 88,134 g. of crudeisobutyl methacrylate from the decanter. This is equivalent to about 980grams of product per cubic inch of Berl saddles. The reactor was shutdown for modification. Examination of the packing showed no sign of anypolymer.

C. The reactor was started up using the larger column described earlier.It was first packed with 220 cubic inches of untreated A" unglazedprocelain Berl saddles. Using the same feed rates and materials asbefore, the reactor ran 25 hours before polymerization in the packedsection forced a shut down. A total of 13,600 grams of crude isobutylmethacrylate had been collected, which is 61.8 grams of product percubic inch of Berl saddles.

D. The packing of the reactor used in above C was then replaced with thesame amount of A1" unglazed porcelain Berl saddles treated as describedin part B. Running at the same feed rates and with the same materials asbefore for 60 days, a total of 239,360 grams of crude isobutylmethacrylate was collected. This is equivalent to 1,090 grams of productper cubic inch of Berl saddles. The reactor was shut down formodification. Examination of the packing did not disclose any polymerformation.

It will be noted from above Examples 1A and C wherein untreated Berlsaddles were employed, that the yield of product was only 57 and 62 g./cubic inch of packing, respectively, before polymerization became severeenough to force a complete shutdown of the reactor. However, when theacid treated Berl saddles were employed as in above Example 113 and D,the yield of product increased to about 890 and 1090 g./cubic inch ofthe treated packing, respectively, before the reactors were shut downfor reasons other than polymerization. Thus, the final capacity of thepacking treated according to the invention to prevent polymerization isnot accurately known, but all the evidence points to an active lifeperiod much greater than 18 times that of the untreated packing.

Example2 Clean unglazed porcelain Berl saddles were covered with amixture prepared from equal volumes of fuming sulfuric acid'(20 percentsulfur trioxide) and concentrated nitric acid. After 12 hours the acidmixture was poured off and the saddles were washed twice with water. Thetreated packing was used in a reactor employed in the preparation ofisobutyl methacrylate by the reaction of isobutanol, water, strongsulfuric acid, and methacrylamide. Phenol and air were used during theprocess to inhibit polymerization in the reboiler section of thereactor. After ten days of continuous operation no polymer was formed inthe packed section of the reactor but on replacing the treated Berlsaddles with untreated Berl saddles and running the unit as before thepacked section of the reactor became plugged with polymer after only 12hours of operation. On replacing the untreated Berl saddles with Berlsaddles treated as described, the reactor was operated for two monthswithout any visible polymer formation in the packed section.

Example 3 Clean unglazed porcelain Berl saddles were covered with amixture prepared from equal volumes of concentrated surfuric acid andconcentrated nitric acid. After 8 hours the mixture was removed from theBerl saddles and the saddles were washed twice with water. The treatedpacking was used to prepare a distillation column for the purificationof methacrylate esters. The distillation column was operated for twomonths without any visible polymer formation. The column operated underidentical conditions but with stainless steel or untreated Berl saddlesquickly became inoperative due to polymer formation.

While the invention has been illustrated in the above examples with justthe preparation of isobutyl methacrylate, will be understood that themethacrylamide intermediate in the examples can be substituted by a likeamount of acrylamide to give the corresponding isobutyl acrylate ingenerally similar good yields/cc. of the acid treated packing. Also, theisobutanol employed in the examples can be replaced with a like amountof any alcohol that is capable of entering into esterification reactionswith acrylic and methacrylic acids. In this regard it is noted that theOH group is the functional group of these alcohols and its reactivity isnot affected even by relatively large radicals such as naphthalene andthe like. Therefore, it is obvious to those skilled in the art that agreat and diverse group of alcohols generally known to esterify acrylicand methacrylic acids may be successfully employed in the presentinvention. Examples of useful straight or branched, saturated aliphaticalcohols are methyl, ethyl, propyl, butyl, isopropyl, sec. butyl, tert.butyl, arnyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl,hexadecyl, 2-methyl-l-butyl, 3-methyl-1-butyl, 3-penty1,2-methyl-1-pentyl, 2-ethyl-1-butyl, 4-methyl-2- pentyl, 2-heptyl,2-ethy1hexyl, Z-octyl, S-ethyl-Z-n-onyl, and2-m'ethyl-7-ethyl-4-undecyl. Other exemplary alcohols are the aromaticor cycloaliphatic alcohols, for example, 'benzyl, phenylethyl,chlorophenyl, cyclohexyl, cyclobutyl, cyclopentyl and the like. Otheruseful alcohols are Z-methoxethyl, 2-ethoxyethyl, Z-butoxyethyl,tetrahydrofurfuryl, o-tolyl, and 2-nitro-2-rnethyl propyl methacrylate.

Thus, the invention has wide applicability for preparing the variousesters of methacrylic and acrylic acids by appropriate selection of thealcohol that is reacted with the mentioned amide in accordance with thefollowing reaction scheme.

CH;=CCOOR Ammonium Salt wherein R stands for the radical of any alcoholwhich can esterify acrylic or methacrylic acid, and R stands forhydrogen or a methyl radical. Also, as hereinbefor e in dicated, theinvention is efiicacious for indefinitely long periods of operationaltime without polymerization difficulties, whereas the older methods onlypartially prevent polymerization. Another advantage of the invention isthat the continuous addition of inhibitor compounds is not required inthe region specified by this invention, i.e. in the reactor column.Further, this invention can be applied to manufacturing processes thatwould destroy or otherwise inactivate many of the usual organicinhibitors. The invention also eliminates the need to practice specialoperational procedures to remove polymer formed during normal operationas is the case with processes using only the conventional inhibitors.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

We claim:

1. A ceramic packing material prepared by pretreatment of an unglazedceramic material selected from silica and silicates, the pretreatmentcomprising soaking the untreated unglazed ceramic packing material in aconcentrated nitric-sulfuric acid mixture for at least about fifteenminutes, at a temperature of about 1560 C., removing the ceramicmaterial from the bath, and rinsing the ceramic material with water.

2. A composition as in claim 1 wherein the nitric-sulfuric acid mixtureconsists essentially of substantially equal volumes of concentratednitric acid and concentrated sulfuric acid.

3. A composition as in claim 1 wherein the nitric-sulfuric acid mixtureconsists essentially of substantially equal volumes of (1) concentratednitric acid and (2) Sulfuric acid containing about 20% free S0 4. Acomposition as in claim 1 wherein the treatment comprises soaking saidunglazed ceramic material in the acid bath for about 12 to 24 hours at atemperature of from about 20 to 30 C.

5. A process for the preparation of the ceramic packing material ofclaim 1 comprising (1) contacting said unglazed ceramic packing materialwith a concentrated nitric-sulfuric acid mixture for at least fifteenminutes and (2) rinsing the ceramic material with Water.

References Cited UNITED STATES PATENTS 2,485,626 10/1949 Mills 252-450 X2,967,156 1/1961 Talvenheimo 252-450 X OTHER REFERENCES WebstersDictionary, G. and C. Merriam Co., 1960, p. 136.

LEON D. ROSDOL, Primary Examiner.

1. GLUCK, Assistant Examiner.

1. A CERAMIC PACKING MATERIAL PREPARED BY PRETREATMENT OF AN UNGLAZEDCERAMIC MATERIAL SELECTED FROM SILICA AND SILICATES, THE PRETREATMENTCOMPRISING SOAKING THE UNTREATED UNGLAZED CERAMIC PACKING MATERIAL IN ACONCENTRATED NITRIC-SULFURIC ACID MIXTURE FOR AT LEAST ABOUT FIFTEENMINUTES, AT A TEMPERATURE OF ABOUT 15-60*C., REMOVING THE CERAMICMATERIAL FROM THE BATH, AND RINSING THE CERAMIC MATERIAL WITH WATER.